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<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.overview.implementation"></a><a class="link" href="implementation.html" title="Platform-Specific Implementation Notes">Platform-Specific
      Implementation Notes</a>
</h3></div></div></div>
<p>
        This section lists platform-specific implementation details, such as the
        default demultiplexing mechanism, the number of threads created internally,
        and when threads are created.
      </p>
<h5>
<a name="boost_asio.overview.implementation.h0"></a>
        <span><a name="boost_asio.overview.implementation.linux_kernel_2_4"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.linux_kernel_2_4">Linux
        Kernel 2.4</a>
      </h5>
<p>
        Demultiplexing mechanism:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            Uses <code class="computeroutput"><span class="identifier">select</span></code> for demultiplexing.
            This means that the number of file descriptors in the process cannot
            be permitted to exceed <code class="computeroutput"><span class="identifier">FD_SETSIZE</span></code>.
          </li></ul></div>
<p>
        Threads:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
            Demultiplexing using <code class="computeroutput"><span class="identifier">select</span></code>
            is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
          </li>
<li class="listitem">
            An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
            is used to emulate asynchronous host resolution. This thread is created
            on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
          </li>
</ul></div>
<p>
        Scatter-Gather:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
            operation.
          </li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h1"></a>
        <span><a name="boost_asio.overview.implementation.linux_kernel_2_6"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.linux_kernel_2_6">Linux
        Kernel 2.6</a>
      </h5>
<p>
        Demultiplexing mechanism:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            Uses <code class="computeroutput"><span class="identifier">epoll</span></code> for demultiplexing.
          </li></ul></div>
<p>
        Threads:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
            Demultiplexing using <code class="computeroutput"><span class="identifier">epoll</span></code>
            is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
          </li>
<li class="listitem">
            An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
            is used to emulate asynchronous host resolution. This thread is created
            on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
          </li>
</ul></div>
<p>
        Scatter-Gather:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
            operation.
          </li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h2"></a>
        <span><a name="boost_asio.overview.implementation.solaris"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.solaris">Solaris</a>
      </h5>
<p>
        Demultiplexing mechanism:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            Uses <code class="literal">/dev/poll</code> for demultiplexing.
          </li></ul></div>
<p>
        Threads:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
            Demultiplexing using <code class="literal">/dev/poll</code> is performed in one
            of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
          </li>
<li class="listitem">
            An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
            is used to emulate asynchronous host resolution. This thread is created
            on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
          </li>
</ul></div>
<p>
        Scatter-Gather:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
            operation.
          </li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h3"></a>
        <span><a name="boost_asio.overview.implementation.qnx_neutrino"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.qnx_neutrino">QNX
        Neutrino</a>
      </h5>
<p>
        Demultiplexing mechanism:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            Uses <code class="computeroutput"><span class="identifier">select</span></code> for demultiplexing.
            This means that the number of file descriptors in the process cannot
            be permitted to exceed <code class="computeroutput"><span class="identifier">FD_SETSIZE</span></code>.
          </li></ul></div>
<p>
        Threads:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
            Demultiplexing using <code class="computeroutput"><span class="identifier">select</span></code>
            is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
          </li>
<li class="listitem">
            An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
            is used to emulate asynchronous host resolution. This thread is created
            on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
          </li>
</ul></div>
<p>
        Scatter-Gather:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
            operation.
          </li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h4"></a>
        <span><a name="boost_asio.overview.implementation.mac_os_x"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.mac_os_x">Mac
        OS X</a>
      </h5>
<p>
        Demultiplexing mechanism:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            Uses <code class="computeroutput"><span class="identifier">kqueue</span></code> for demultiplexing.
          </li></ul></div>
<p>
        Threads:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
            Demultiplexing using <code class="computeroutput"><span class="identifier">kqueue</span></code>
            is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
          </li>
<li class="listitem">
            An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
            is used to emulate asynchronous host resolution. This thread is created
            on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
          </li>
</ul></div>
<p>
        Scatter-Gather:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
            operation.
          </li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h5"></a>
        <span><a name="boost_asio.overview.implementation.freebsd"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.freebsd">FreeBSD</a>
      </h5>
<p>
        Demultiplexing mechanism:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            Uses <code class="computeroutput"><span class="identifier">kqueue</span></code> for demultiplexing.
          </li></ul></div>
<p>
        Threads:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
            Demultiplexing using <code class="computeroutput"><span class="identifier">kqueue</span></code>
            is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
          </li>
<li class="listitem">
            An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
            is used to emulate asynchronous host resolution. This thread is created
            on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
          </li>
</ul></div>
<p>
        Scatter-Gather:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
            operation.
          </li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h6"></a>
        <span><a name="boost_asio.overview.implementation.aix"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.aix">AIX</a>
      </h5>
<p>
        Demultiplexing mechanism:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            Uses <code class="computeroutput"><span class="identifier">select</span></code> for demultiplexing.
            This means that the number of file descriptors in the process cannot
            be permitted to exceed <code class="computeroutput"><span class="identifier">FD_SETSIZE</span></code>.
          </li></ul></div>
<p>
        Threads:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
            Demultiplexing using <code class="computeroutput"><span class="identifier">select</span></code>
            is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
          </li>
<li class="listitem">
            An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
            is used to emulate asynchronous host resolution. This thread is created
            on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
          </li>
</ul></div>
<p>
        Scatter-Gather:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
            operation.
          </li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h7"></a>
        <span><a name="boost_asio.overview.implementation.hp_ux"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.hp_ux">HP-UX</a>
      </h5>
<p>
        Demultiplexing mechanism:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            Uses <code class="computeroutput"><span class="identifier">select</span></code> for demultiplexing.
            This means that the number of file descriptors in the process cannot
            be permitted to exceed <code class="computeroutput"><span class="identifier">FD_SETSIZE</span></code>.
          </li></ul></div>
<p>
        Threads:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
            Demultiplexing using <code class="computeroutput"><span class="identifier">select</span></code>
            is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
          </li>
<li class="listitem">
            An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
            is used to emulate asynchronous host resolution. This thread is created
            on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
          </li>
</ul></div>
<p>
        Scatter-Gather:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
            operation.
          </li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h8"></a>
        <span><a name="boost_asio.overview.implementation.tru64"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.tru64">Tru64</a>
      </h5>
<p>
        Demultiplexing mechanism:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            Uses <code class="computeroutput"><span class="identifier">select</span></code> for demultiplexing.
            This means that the number of file descriptors in the process cannot
            be permitted to exceed <code class="computeroutput"><span class="identifier">FD_SETSIZE</span></code>.
          </li></ul></div>
<p>
        Threads:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
            Demultiplexing using <code class="computeroutput"><span class="identifier">select</span></code>
            is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
          </li>
<li class="listitem">
            An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
            is used to emulate asynchronous host resolution. This thread is created
            on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
          </li>
</ul></div>
<p>
        Scatter-Gather:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            At most <code class="computeroutput"><span class="identifier">min</span><span class="special">(</span><span class="number">64</span><span class="special">,</span><span class="identifier">IOV_MAX</span><span class="special">)</span></code> buffers may be transferred in a single
            operation.
          </li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h9"></a>
        <span><a name="boost_asio.overview.implementation.windows_95__98_and_me"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.windows_95__98_and_me">Windows
        95, 98 and Me</a>
      </h5>
<p>
        Demultiplexing mechanism:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            Uses <code class="computeroutput"><span class="identifier">select</span></code> for demultiplexing.
          </li></ul></div>
<p>
        Threads:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
            Demultiplexing using <code class="computeroutput"><span class="identifier">select</span></code>
            is performed in one of the threads that calls <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
          </li>
<li class="listitem">
            An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
            is used to emulate asynchronous host resolution. This thread is created
            on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
          </li>
</ul></div>
<p>
        Scatter-Gather:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
            For sockets, at most 16 buffers may be transferred in a single operation.
          </li></ul></div>
<h5>
<a name="boost_asio.overview.implementation.h10"></a>
        <span><a name="boost_asio.overview.implementation.windows_nt__2000__xp__2003_and_vista"></a></span><a class="link" href="implementation.html#boost_asio.overview.implementation.windows_nt__2000__xp__2003_and_vista">Windows
        NT, 2000, XP, 2003 and Vista</a>
      </h5>
<p>
        Demultiplexing mechanism:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
            Uses overlapped I/O and I/O completion ports for all asynchronous socket
            operations except for asynchronous connect.
          </li>
<li class="listitem">
            Uses <code class="computeroutput"><span class="identifier">select</span></code> for emulating
            asynchronous connect.
          </li>
</ul></div>
<p>
        Threads:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
            Demultiplexing using I/O completion ports is performed in all threads
            that call <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">poll_one</span><span class="special">()</span></code>.
          </li>
<li class="listitem">
            An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
            is used to trigger timers. This thread is created on construction of
            the first <code class="computeroutput"><span class="identifier">deadline_timer</span></code>
            or <code class="computeroutput"><span class="identifier">deadline_timer_service</span></code>
            objects.
          </li>
<li class="listitem">
            An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
            is used for the <code class="computeroutput"><span class="identifier">select</span></code>
            demultiplexing. This thread is created on the first call to <code class="computeroutput"><span class="identifier">async_connect</span><span class="special">()</span></code>.
          </li>
<li class="listitem">
            An additional thread per <code class="computeroutput"><span class="identifier">io_service</span></code>
            is used to emulate asynchronous host resolution. This thread is created
            on the first call to either <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">async_resolve</span><span class="special">()</span></code>.
          </li>
</ul></div>
<p>
        Scatter-Gather:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
            For sockets, at most 64 buffers may be transferred in a single operation.
          </li>
<li class="listitem">
            For stream-oriented handles, only one buffer may be transferred in a
            single operation.
          </li>
</ul></div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2012 Christopher M. Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
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